What is the function of a stem cell give a simple answer i dont want it to be overcomplicated like my revsion guide

Select all the true statements about the cosmic microwave background radiation

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic